"New game plus - quests will have no rewards..."

[Melichoir]

I don't quite see any point in SE's decision to divide it into "chapters" (whatever that is), when it's already subdivided into quests.

It's likely divided into chapters for ease and less clutter. There something like...350ish quests atleast in the MSQ I think. And people generally dont remember specific quest names, they remember the broader events. So organizing by chapter makes sense cause you can sum up a quest chain by chapter and people will pick up on that pretty readily rather than reading each quest summary.